This section is intended to provide a background or context to the invention recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Minimally invasive medical procedures with image guidance for needle access to anatomic structures are becoming increasingly common and important to the clinical management of patients. As illustrated in FIGS. 1A-1F, image guidance can be used for many different needle-based procedures including CT-guided pulmonary nodule (A), retroperitoneal lymph node (B) or sacral bone biopsies (C). CT-guidance also is demonstrated for a transgluteal abscess drainage (D) and radiofrequency ablation of a right kidney renal cell carcinoma (E). Other image modalities, such as fluoroscopy, also guide needle placement including lumbra puncture (F, AP projection) for cerebrospinal fluid studies, intrathecal chemotherapy or a subsequent CT myelogram. In 2008, the annual rate of image-guided biopsies increased to 1.945 per 100,000 Medicare enrollees (almost 2% per capita). See Kwan et al., “Effect of Advanced Imaging Technology on How Biopsies Are Done and Who Does Them,” 256(3) Radiology 751 (2010), the entire contents of which are hereby incorporated by reference. For example, the University of California, San Francisco (UCSF) Department of Radiology & Biomedical Imaging currently performs 50-100 image-guided procedures each week. These image-guided procedures generate significant revenue for hospitals and physician practices.
CT image guidance improves visualization of the tissue target during a variety of medical interventions including biopsies, radiofrequency ablations, pain procedures and other interventions. CT-guided procedures are minimally invasive, can reach small deep tissue structures in or surrounded by bone, require minimal patient recovery, decrease healthcare costs and immediately impact clinical management. However, CT-guided procedures still risk inadvertent tissue injury and have longer procedure times than fluoroscopy or ultrasound-guided procedures. Moreover, there may a patient may be concerned regarding the associated radiation use in CT-guided procedures. These potential limitations are mitigated by operator training, skill and experience performing CT-guided procedures. The most common current practice for CT-guided procedures involves iterative readjustment of needle position with focused repeat CT imaging of the patient.
Percutaneous image-guided procedures in which access to inner organs or other tissue is done via needle-puncture of the skin share a common protocol: after initial images are obtained, an operator determines a safe surface entry point, trajectory angle and penetration distance for a manually-directed needle to reach a target organ or tissue. In CT-guided procedures, establishing the best surface entry point for the procedure works well using a standard metallic fiducial and grid (see FIG. 2) and penetration distance is easy to measure with images. For example, FIG. 2 illustrates a typical process for a CT-guided procedure demonstrated for a left L4 transforaminal epidural block for lower back pain. In this procedure, a patient is placed prone, and then CT images are obtained in a region of interest with a radio-opaque grid on a surface of the patient (“1st Scout”). Operators use these images to plan an optimal needle trajectory to reach an anatomic target which includes consideration of needle angle and depth. The surface entry for the needle is verified with a metallic fiducial bead (“2nd Scout”). The operator then places the needle, which is slowly advanced (“Guide”) and adjusted as needed using CT guidance until the target is reached and verified with contrast injection (“Contrast”). Although the protocol for establishing a target trajectory angle and penetration distance is common, prescribing and maintaining a correct needle angle is more challenging in daily practice. This is due in part to the fact that image orientations generated by the CT scanner, for example, are relative to the scanner and procedure room floor. Thus, the operator plans the angles with respect to the images, as opposed to planning the angles with respect to the patient who might be positioned in a slight oblique orientation to the scanner or floor to enhance their comfort.
FIG. 3 illustrates an example of an appropriate angle for needle position prior to penetrating the surface of the patient in terms of target angles and horizon angles. In particular, FIG. 3 illustrates a simplified schematic of a typical CT-guided needle biopsy (not drawn to scale). In FIG. 3, the left and right panels demonstrate axial and coronal projections, respectively. In this example, a target must be approached at an angle to avoid other important anatomic structures that are labeled “Avoid”). An angle between the needle trajectory and a vertical line from the target lesion (plumb or perpendicular to the floor) is called the “target angle”. In this example, the target angle is 45 degrees. An angle between an opposite needle end (with a hub) and a line parallel to the floor is called the “horizon angle” and should be equal to 180 degrees minus the target angle. In this example, the horizon angle is 135 degrees. In FIG. 3, s is the surface distance from vertical plumb line and d is the depth of penetration to the target.
The current practice is to maintain the target angle in the axial plane while angling in the z-axis is avoided (i.e., the needle remains straight in the coronal projection) as the needle is advanced deeper towards the target. Direct vertical or horizontal orientations for needle placement without oblique angulation are simpler, but have relationships to the floor that the operator also must maintain as the needle is advanced (i.e., horizon angles of 90 and 0 degrees, respectively). Thus, the primary challenge is to prevent or minimize discordance between the planned needle trajectory (see FIG. 3) and an actual needle course throughout the image-guided procedure.
Needle deviations or needle angle errors that occur at or near the skin surface often only become apparent once the needle has traversed deep into the patient. Without any visual reference, the operator may unconsciously alter a correct needle angle or deviate further from the correct needle angle as it is advanced deeply or as the needle encounters tissue interfaces. Correction of a needle angle at depth is only possible for small needle angle errors, as corrections often require withdrawal, adjusted needle angle and reinsertion. This process may require several iterations that further increase tissue injury. Thus, it is critical to get the needle angle correct while the needle is at the surface or only superficially placed within the tissue.
Needle deviations remain common for several reasons. First, the operator must translate angle and depth measurements on the 2-dimensional axial CT images onto an accurate needle target angle on the surface of a patient (with some respiratory motion even when the patient is cooperative). Second, because it is not always possible to view the needle directly orthogonal to the floor or axis of the CT scanner during the procedure, parallax error also can affect true needle position. Third, as the needle is advanced, changes in tissue density (e.g. between fat and muscle) can deflect the needle. The likelihood of encountering error in the actual needle course increases when the target structure is small and/or deeper from the surface, yet these circumstances are often the reason for using image guidance in cases such as a 10-mm retroperitoneal lymph node adjacent to the abdominal aorta 12 cm deep to the surface similar to FIG. 1B.
To minimize error, needle trajectories are planned to be true vertical or horizontal if at all possible. See, e.g., FIG. 1A. When angulated trajectories are necessary to avoid other anatomic structures, the angle is prescribed in only one plane (usually the axial plane as illustrated in FIG. 3) to minimize the potential for compounding error. There are two common ways a needle deviates from the planned trajectory that occur either in isolation or together, hereafter referred to as X-tilt and Z-tilt. As seen in FIG. 4, X-tilt (1st column) occurs when the needle enters the patient too steep (1) or shallow (2) in the axial plane with respect to the planned ideal trajectory (dashed line) to reach the target. Incorrect needle position for X-tilt is recognized in the axial projection, but the other projections usually look normal on images the operator can obtain. For example, subtle needle shortening or lengthening can be difficult to recognize in the coronal projection. Z-tilt (2nd column) occurs when the needle enters the patient with an abnormal angle towards the feet (caudal (3)) or head (cranial (4)) with respect to the planned trajectory. Z-tilt is most evident in the coronal and sagittal projections, but can often be seen in the axial plane when the entire needle is not visualized (e.g. missing superficial needle component in FIG. 1E). These errors are only recognized with imaging in certain planes after they occur.
The magnitude and frequency of needle deviations are subject to an operator's spatial reasoning ability, experience and hand-eye coordination, yet needle position often must be adjusted during the procedure. With the current state of the art, this is an expected component of the procedure at least somewhat mitigated by using image guidance, however the iterative adjustment of needle position and advancement has some disadvantages. Needle placement error can injure anatomic structures leading to undesirable hemorrhage and/or vascular, solid organ or bowel injury. More commonly, needle repositioning increases the volume of tissue traversed by the procedure needle leading to more tissue injury and/or patient pain. Adjustments increase procedure time, which affects patient comfort and the duration of the patient's exposure to conscious sedation, as well as decreased throughput to the detriment of patient wait times and practice revenue. Adjustments also require more imaging, which in the context of x-ray or CT guidance, increases a patient's exposure to ionizing radiation. Finally, the procedure can fail to sample the desired target for treatment or diagnosis.
Many technical solutions have been proposed to improve the safety and efficiency of image guidance during medical procedures over the past 25 years. These include various handheld, stereotactic or robotic devices; augmented visual overlay; and laser, electromagnetic or camera tracking guidance. Although these solutions propose innovative methods for improving the safety and efficacy of image-guided interventions, many of these solutions are expensive or not widely available, and have so far proven difficult to realize widely in clinical practice.
The current state of the art is to direct needle placement using an iterative cycle of needle movement and image guidance, but there is a delay in feedback to the operator from imaging after the needle is manipulated. In typical guidance devices, the device holds the needle and prescribes the angle in that the operator inserts the needle through the device, instead of relying on the operator to keep the angle steady by hand.
Robotic systems have been proposed to be placed next to the patient in the imaging suite, but these are designed more to replace or supplement for an experienced operator rather than enhance their abilities. A separate robotic system may prove cumbersome, complicated, expensive and unable to adjust for patient movement during the procedure without repeat setup imaging. Similarly, “brain lab” navigation systems are in common use, for example, at UCSF for neurosurgery. However these brain lab navigation systems require extensive preoperative imaging, significant computation and modeling prior to procedures with stereotactic equipment. This is inconsistent with the typical patient presentation and workflow for procedures outside brain tumor resection. These systems are expensive to implement and require additional imaging on a separate occasion. Further, unlike the brain, other regions of the body have more periodic movement over the time that would degrade preparative imaging for these systems. Many image-guided procedures also are done on patients who may not be amenable to the highly controlled settings required for the pre-procedure imaging.
Laser fiducials on the needle have been proposed, but these may require a target for the laser projection that may need to be away from the patient or become cumbersome overlying the site of the procedure.
Real-time ultrasound guidance may work, but only on superficial soft tissue anatomic targets in non-obese subjects. Ultrasound-guidance is extremely limited in regions that contain or adjacent to air or bone.
A need exists for improved technology that is more practical and allows for improvement of the precision and speed of image-guided needle placement to minimize the risks of needle deviations from the planned trajectory.